Preparation of thiolesters from aliphatic acid anhydrides and aromatic thiols



United States Patent Mo., assignor to Monsanto Company, St.

Louis, Mo., a corporation of Delaware N0 Drawing. Filed July 15, 1965, Ser. No. 472,341 8 Claims. (Cl. 260-455) ABSTRACT OF THE DISCLOSURE A process for the preparation of a thiolester by reacting an aliphatic acid anhydride with an aromatic thiol in the presence of a catalytic amount of a tertiary amine.

This invention relates to an improved process for the preparation of thiolesters. More particularly it relates to a process wherein saturated aliphatic acid anhydrides are reacted with aromatic thiols in the presence of relatively small amounts of certain bases to form thiolesters.

It is known to produce thiolesters by reacting thiols with acid anhydrides; however, these known processes use at least an equimolar amount of a base, such as pyridine, triethylamine and the like; and, in some of these heretofore known processes, an excess of the equimolar amount of base is specified. The consumption of relatively large amounts of base results in relatively high production cost which is a major disadvantage of the known processes.

It is believed, therefore, that a process for the production of thiolesters from aromatic thiols and aliphatic anhydrides, which process uses only a catalytic amount of base and which process gives high yields, is a significant advance in the art.

It is an object of this invention to provide an improved process for the production of aromatic thiolesters.

It is a further object of this invention to provide a high yield process for the production of aromatic thiolesters wherein said thiolesters are produced by an essentially direct reaction of an aromatic thiol with an anhydride.

Other objects, advantages, and features of this invention will become readily apparent to those skilled in the art from the detailed description which follows.

It has been discovered that aromatic thiols will react with aliphatic acid anhydrides to form aromatic thiolesters in the presence of only a catalytic amount of certain bases. The high yields obtained with the process of this 0 invention, which uses only a catalytic amount of certain bases, are completely unexpected in view of the heretofore known processes which specify the need for at least an equimolar amount of base. The process of this invention is also unobvious because at least an equimolar amount of base is required to achieve esterification when aliphatic thiols and aliphatic acid anhydrides are used.

The saturated aliphatic anhydrides which are useful in the practice of this invention are those of the formula:

wherein R and R are each alkyl containing from 1 to 12 carbon atoms.

When the unsymmetrical anhydrides, that is, those anhydrides wherein R and R are different alkyls, are used, mixtures of the corresponding thiolesters are produced. Similarly, when a mixture of aliphatic anhydrides is used, a mixture of thiolesters is also produced. The mixtures of thiolesters thus produced require subsequent separation to obtain relatively pure individual products. Since any thiolester which is produced from either an unsymmetrical anhydride or a mixture of anhydrides can also be produced from the suitable symmetrical anhydride, it is preferred to use symmetrical acid anhydrides, that is, those anhydrides wherein R and R are the same alkyl.

Compounds illustrative of said useful symmetrical aliphatic acid anhydrides include ethanoic acid anhydride, propanoic acid anhydride butanoic acid anhydride, pentanoic acid anhydride, hexanoic acid anhydride, heptanoic acid anhydride, octanoic acid anhydride, decanoic acid anhydride, dodecanoic acid anhydride and the anhydrides of the corresponding isomeric acids.

The aromatic thiols or mercaptans which are useful in the practice of this invention can be represented by the formula:

wherein R is a member selected from the group consisting of phenylene and lower alkylated phenylene, and X is a member selected from the group consisting of hydrogen, chlorine, bromine, nitro, acetamido and lower alkoxy. It is to be noted that, as used herein, lower alkylated phenylene and lower alkoxy mean that the alkyl portion of the radical is a lower alkyl group, that is, an alkyl group containing from 1 to 4 carbon atoms.

Compounds which are illustrative of said useful thiols include mercaptobenzene, Z-chloro-mercaptobenzene, 3- chloro-mercaptobenzene, 4-chloro-mercaptobenzene, 2-mitro-mercaptobenzene, 4-nitro-mercaptobenzene, 4-methoxy-mercaptobenzene, 3-ethoxy-mercaptobenzene, 4-propoxy-mercaptobenzene, 4-acetamido-3-mercaptotoluene, 3- mercaptotoluene, 4-mercaptotoluene, 3-chloro-4-mercaptotoluene, 3-nitro-4-mercaptotoluene, 3-ethoxy-4-mercaptotoluene, 1-n-butyl-3-chloro-4-mercaptobenzene, 3-bromo- 4-mercapto-cumene and 3-nitro-4-n-propyl-mercaptobenzene.

Although the molar ratio of aromatic thiol to aliphatic acid anhydride can be varied throughout a relatively wide range, such as from about 1:1000 to about 100021, and still produce at least some of the aromatic thiolester, it is preferred for economy and optimum yield to approximate molar equivalents of reactants; that is, one mole of aromatic thiol per mole of aliphatic acid anhydride.

Generally, the acid anhydrides are liquids within the temperature range employed in the practice of this invention and will dissolve the aromatic thiols, thus eliminating the need for an extrinsic solvent. Although temperature is not critical, for ease of operation and for optimum yields, it is preferred to operate within the temperature range of from about 10 C. above the freezing point to about 5 C. below the boiling point of the solution of the thiol in the anhydride. Since, in most cases, a temperature range of from about 20 C. to about C. can be used, this relatively moderate range is especially preferred.

In general, those bases which (a) are soluble in the solution of thiol in the anhydride, (b) do not react with either the anhydride, thiol or thiolester and (c) have sufiicient basic properties to catalyze the reaction can be used in the practice of this invention. The compounds which have been found to have the foregoing suitable properties are those selected from the group consisting of pyridine, lower alkylated pyridine and tertiary amines of the formula R the IQ! wherein R, R and R" are each lower alkyl.

Compounds illustrative of said useful bases include triaromatic thiolesters are prepared from aromatic thiols ethylamine, tripropylamine, tributylamine, ethylisoproand aliphatic acid anhydrides. Selected examples of such pylmethylamine, dimethylethylamine, di-isobutylmethylpreparations are given in the following table.

Ex. TlliOl Acid Anhydrldc Tertiary Amine Thiolcster 3 4-nitro-mercaptobcnzcnc 4nitr0phcnyl thioldodecanoate. 4 3-chloro-4rnercaptot0lucne Butanoic oc1danhydride. 2-chloro-p-tolyl thiolbutanoatc. 5 LbromoA-mercaptobenzone.- Propanoic acid anhydnde.. Triethylarnine 4-brornophenyl thiolpropionate. G 4-acctamido-3-mcrcapt0tolucne Ethanoic acid anhydride. Tributylamine Z-acctamido-m-tolyl thiolacctatc. 7 -methoxy-mcrcaptobcnzenc Hcptanoic acid anhydride Dimethylethylamina. 4-mcthoxyphenyl thiolhcptanoatc. 8 3-chloro-mercaptobenzone Butanoic acid anhydride Tripropylamine 3-chlorophenyl thiolbutanoate. 9 4-dimctl1ylamino mcrcapt0benzene. Dccanoic acid anhydride 2-methylpyridinc 4-dimcthylaminopheuyl thioldecanoate. 10 3-cthoxydmercaptotoluene Octanonic acid anhydride Di-isobutylmethyla- Z-cthoxy-p-tolyl thioloctanoatc.

1111116. 11. 3-chlor0-4-isopropyl-rnercapto- Propauoic acid anhydride Tributylamine 3-chloro-4-isopropylpltenyl benzene. thiolpropionate. l2"... 2-cl1loro-n1ercaptobenzcne Hexanoic acid anhydride Trietliylamine 2-chlorophenyl thiolliexanoate. 13. 4-mercaptotolucnc Pentanoic acid anhydride Ethylisobutylmethylp-Tolyl thiolpentanoate.

amine.

14... d-n-butyl-rnorcaptobcnzcne Ethanoic acid anhydride Triethylamine 4n-butylpl1eny1 thiolacetatc. 5 B-ethoxy mercaptobenzeno Butanonic acid anhydride ..do 3-eth0xyphenyl tliiolbutanoate.

amine, pyridine, Z-methylpyridine, 3-rnethylpyridine, 2- While the invention has been described herein with repropylpyridine, 2,4-dimethylpyridine, Z-ethylpyridine, 4- gard to specific embodiments, it is not so limited. It is isopropylpyridine, 2,4,6-trimethylpyridine. to be understood that variations and modifications there- The reaction of this invention can be conducted using of may be made by those skilled in the art without departamounts of base as low as about 0.01% based upon the ing from the spirit and scope of the invention. weight of the thiol. In most instances, however, it is pre- What is claimed is: ferred to use between about 0.1% and about 3% of said 20 1. In a process for the production of thiolesters wherebase based upon the weight of the thiol to insure emcient in an aliphatic acid anhydride of the formula, reactions. It is completely unexpected that such a signifi- O cant reduction in the amount of base can be made in view H of the prior art which teaches that at least equimolar 3O quantities of bases must be used. When compared with 0 prior processes, a vast reduction in the amount of base is achieved resulting in a major improvement in the process. Larger amounts of bases can be employed but are not preferred since the excess usage serves no purpose except wherein R1 and R2 are each alkyl containing f 1 to to need1eS51y1r}Creasethe Costof the f 12 carbon atoms is reacted with an aromatic thiol of The following examples further lllustrate the lnvenh f 1 t e ormu a, tron. All parts, percentages and proportions are by we1ght unless otherwise indicated. a-

EXAMPLE 1 40 wherein R is a member selected from the group consisting of phenylene and lower alkylated phenylene; and 4'chlomphenyl thlolacetate X is a member selected from the group consisting of hy- About 1,440 parts of 1-chloro-4-mercaptobenzene are dfogeu, chlofiue, bromine, uitro, u t u charged into a conventional reaction vessel equipped with l y p f coulpnsulg f g 531d an agitator. While agitating, about 1,020 parts of ethanoic allphatlc acld auhydflde and stud aromatlc thlOl m the acid anhydride are dissolved in the 1-chloro-4-mercapto- PreseuCe of P about (101% to about 30% y Welght, benzene. After about 10 parts of triethylamine are added, based p u Of a base t pm t an exothermic reaction occurs. Fractional distillation of group conslstmg of py f lower alkylated PY and the crude product, after the reaction is complete-d, yields lower alkyl ternary about 1,690 parts of a product having a boiling point of A p f as defined 1n Clalm 1 hcrem said base 142 C. at 15 mm. Hg and a melting point of 31-32" C. is present 1n amounts of from at least about 0.1% to The infrared absorption spectrum has the expected carabout 0% by W ight ased upon said aromatic thiol. bonyl absorption band of 1680 to 1704 cmr The 3. A process as defined 1n cla1m 1 wherein said base is pound is identified as 4-chlorophenyl thiolacetate, and tfiethylamiuethe yield, based upon the raw materials charged, is about ;d P100655 as defined 111 Clalm 1 Whe em sald base 18 91%. pyn me.

5. In a process for the production of thiolesters where- EXAMPLE 2 in a symmetrical aliphatic acid anhydride of the formula, Phenyl thiolacetate About 1,020 parts of ethanoic acid anhydride are ll charged into a conventional reaction vessel equipped 2-0 with an agitator. While agitating, about 1,100 parts of 0 mercaptobenzene are dissolved in the ethanoic acid anhydride. About 2 parts of triethylamine are added, and

an exothermic reaction occurs with the temperature rising to about After the temperature rise has ceased, wherein Z is alkyl containing from 1 to 12 carbon atoms the reaction product is distilled yielding about 1,370 parts i reacted with an aromatic thiol of the formula,

of a product having a boiling point of 60 C. at 0.5 mm.

Hg. The infrared absorption spectrum gives the expected X R3' SH carbonyl band of from about 1,684 to 1,704 cm." Anawherein R is a member selected from the group con- II o lytical determination of elemental content indicates the sisting of phenylene and lower alkylated phenylene, and formula of the product to be C H OS. The yield of phenyl X is a member selected from the group consisting of hythiolacetate is about 90% based upon the reactants drogen, chlorine, bromine, nitro, acetamido and lower charged. alkoxy, the improvement comprising reacting said Following the procedure of Examples 1 and 2, other aliphatic acid anhydride and said aromatic thiol in the 5 presence of from about 0.01% to about 3.0% by weight, based upon said aromatic thiol, of a base selected from the group consisting of pyridine, lower alkylated pyridine and lower alkyl tertiary amines.

6. A process as defined in claim 5 wherein said base is present in amounts of from about 0.1% to about 3.0% by weight based upon said aromatic thiol.

7. A process as defined in claim 6 wherein said base is triethylamine.

8. A process as defined in claim 6 wherein said base is pyn'dine.

References Cited Schleppnik et al., J. Org. Chem, vol. 29, pp. 1663, 1910-1915 (1964).

CHARLES B. PARKER, Primary Examiner. D. R. PHILLIPS, Assistant Examiner. 

